1. Field of Invention
The present invention relates to an active matrix substrate on which transistors are formed, an electrooptical device using this active matrix substrate, and a method of producing the active matrix substrate. More particularly, the present invention relates to a technique of forming a film quality evaluation region for evaluating films used to form transistors.
2. Description of Related Art
A representative active matrix substrate on which transistors and signal lines are formed is one for use in a liquid crystal display (electrooptical device). Some active matrix substrates of this type include a driving circuit disposed thereon. In this case, a plurality of scanning lines and data lines are disposed on an insulating substrate, and furthermore, a plurality of pixels are disposed in the form of an array at intersections of the scanning lines and data lines. Each pixel includes a pixel electrode and a pixel switching thin film transistor (hereafter referred to as a TFT) connected to a scanning line and a data line. On the insulating substrate, in an area outside an image display area, there are disposed a data line driving circuit for supplying an image signal to the respective data lines and a scanning line driving circuit for supplying a scanning signal to the respective scanning lines. These driving circuits are formed of a plurality of TFTs.
Of these TFTs, each TFT for switching a pixel includes, as shown in FIGS. 5(A) and 5(B), a gate electrode 3a formed simultaneously with the scanning lines, source regions 1f and 1d electrically connected via a first contact hole 4a formed in a first interlayer insulating film 4 to a source electrode 6a which is a part of a data line 30, drain regions 1g and 1e electrically connected via a second contact hole 4a formed in the first interlayer insulating film 4 to a drain electrode 6a which is formed of an aluminum film, or the like, simultaneously with the data lines 30. A second interlayer insulating film 7 is formed in a layer above the first interlayer insulating film 4. A third contact hole 8a is formed in this second interlayer insulating film 7, and a pixel electrode 9a is electrically connected to the drain electrode 6d via the third contact hole 8a. The structure described above is also employed for TFTs used to form the driving circuits.
In the active matrix substrate, when various elements, such as the TFT 50 have been formed using a semiconductor process, various characteristics are tested. If the active matrix substrate fails this test, various analyses are performed and the result is fed back. For example, analyses are performed in terms of the impurity concentrations of the source and drain regions and crystallinity of the channel region 1a. Conventionally, such an analysis is performed as follows. First, the surface of the sample, on which the TFTs 50 for switching pixels or used in the driving circuits, is lustered so as to successively remove the second interlayer insulating film 7, the first interlayer insulating film 4, the gate electrode 3a, and the gate insulating film 2, until the channel 1a or the source/drain region is exposed. Thereafter, elemental analysis by way of SIMS (secondary ion mass spectrometory) or X-ray analysis is performed.
In the conventional method of analyzing the source/drain region or the channel region 1a, a long time is needed to remove the second interlayer insulating film 7, the first interlayer insulating film 4, the gate electrode 3a, and the gate insulating film 2. Although the thickness of a film to be analyzed is as small as 50 nm to 100 nm, it is required to remove an interlayer insulating film having a thickness as large as 1 xcexcm. To analyze the channel region 1a, it is required to remove the gate electrode 3a with a thickness of 400 nm. Another problem is that high-accuracy analysis is difficult because the channel region 1a of the TFT 50 which is finally exposed after performing long-time lustering has a small area of at most 100 xcexcm square.
In view of the above, the present invention to provides an active matrix substrate which allows the film quality of a transistor, such as a TFT, to be evaluated easily and accurately, and also provides an electrooptical device using such an active matrix substrate.
The present invention also provides a method of producing an active matrix substrate having a film quality evaluation region which is formed through substantially the same process as that through which a film of a transistor is formed, without needing an additional process, thereby making it possible to accurately evaluate film quality.
According to the present invention, as described above, there is provided a film quality evaluation region in which a semiconductor film for film quality evaluation is formed of the same layer as the semiconductor film used to form a transistor. Alternatively, a semiconductor film for film quality evaluation and a gate insulating film for film quality evaluation are formed using the same layers as a channel region and a gate insulating film, respectively, of a transistor, whereby the film quality evaluation, such as elemental analysis or crystallinity analysis, of the semiconductor film forming the channel region or the source/drain region of the transistor or an impurity distribution at an interface between the gate insulating film and the channel region, can be performed by analyzing the film quality evaluation region.
In the analysis using the film quality evaluation region, unlike the analysis performed directly upon the transistor, it is possible to immediately start the analysis without having to remove the interlayer insulating film and the gate electrode, because the film quality region is exposed through the opening formed through the interlayer insulating film which is formed in the evaluation region simultaneously with the interlayer insulating film in the transistor region. This makes it possible to easily evaluate the film quality in a short time. The film quality evaluation region can be formed over a large area without influencing the characteristics of the transistor. The large film quality evaluation region allows high-accuracy analysis for various items.
According to an aspect of the present invention, to achieve the above objects, there is provided an active matrix substrate that may include a transistor and a signal line both formed on a substrate. The active matrix substrate may further include a film quality evaluation region including a semiconductor film for film quality evaluation, the semiconductor film for film quality evaluation being formed of the same layer as a semiconductor film used to form the transistor, the film quality evaluation region being disposed at one or more locations on the substrate at which neither the transistor nor the signal line is formed. In the following description, a MIS (metal insulator semiconductor) transistor is employed as the transistor. Note that the MIS transistor is not limited to those whose gate is formed of a metal, but those whose gate is formed of a conductive silicon or any other similar material.
In this active matrix substrate according to the present invention, it is desirable that the semiconductor film for film quality evaluation be exposed through an opening formed in an interlayer insulating film in the evaluation region, the interlayer insulating film in the evaluation region being formed of the same layer as an interlayer insulating film formed above the transistor.
In this active matrix substrate according to the present invention, because the semiconductor film for film quality evaluation is formed in the film quality evaluation region using the same layer as the semiconductor film used to form the transistor, analysis, such as elemental analysis or crystallinity analysis, of the semiconductor film forming the channel region and the source/drain region of the transistor can be performed by analyzing the film quality evaluation region. In the analysis using the film quality evaluation region, unlike the analysis performed directly upon the transistor, it is possible to immediately start the analysis without having to remove the interlayer insulating film and the gate electrode, because the film quality region is exposed through the opening formed through the interlayer insulating film which is formed in the evaluation region simultaneously with the interlayer insulating film in the transistor region. This makes it possible to easily evaluate the film quality in a short time. The semiconductor film for film quality evaluation can be formed so as to have a large area in the film quality evaluation region without influencing the characteristics of the transistor. The large film quality evaluation region allows high-accuracy analysis for various items.
In the active matrix substrate according to the present invention, the semiconductor film for film quality evaluation may be formed of the same layer as a source/drain region of the transistor and doped with the same impurity at the same concentration as the source/drain region.
To produce the active matrix substrate having the above-described structure, after forming a semiconductor film used to form the transistor and simultaneously forming the semiconductor film for film quality evaluation in a region to be used as the film quality evaluation region, and then forming a gate insulating film used to form the transistor and simultaneously forming a gate insulating film in the region to be used as the film quality evaluation region, a process is performed which includes the steps of: forming a conductive film used to form a gate electrode of the transistor and then patterning the conductive film so as to form the gate electrode and simultaneously removing the conductive film from the film quality evaluation region; selectively introducing an impurity into the semiconductor film via the gate insulating film so as to form source and drain regions of the transistor and simultaneously introducing the impurity also into the semiconductor film for film quality evaluation via the gate insulating film in the evaluation region; forming the interlayer insulating film in a layer on the surface of the gate electrode and simultaneously forming the interlayer insulating film in the evaluation region, in a layer on the surface of the gate insulating film in the evaluation region; and forming a contact hole, for connection to the transistor, in the interlayer insulating film and simultaneously forming, in the film quality evaluation region, the opening in the interlayer insulating film in the evaluation region and in the gate insulating film in the evaluation region so that the semiconductor film for film quality evaluation is exposed.
In this production method, the semiconductor film for film quality evaluation has substantially the same process history as the source and drain regions of the transistor, and thus the film quality of the source and drain regions of the transistor can be accurately evaluated by analyzing the semiconductor film for film quality evaluation. Furthermore, in this production method, the film quality evaluation region can be formed using the production steps of producing the transistor without needing an additional step.
In the present invention, the source/drain region of the transistor may include a lightly doped source/drain region and a heavily doped source/drain region. In this case, the semiconductor film for film quality evaluation may be formed of the same layer as one of the lightly doped source/drain region and the heavily doped source/drain region, and the semiconductor film for film quality evaluation may be doped with the same impurity at the same concentration as the one of the lightly doped source/drain region and the heavily doped source/drain region.
To produce the active matrix substrate having the above-described structure, after forming a semiconductor film used to form the transistor and simultaneously forming the semiconductor film for film quality evaluation in a region to be used as the film quality evaluation region, and then forming a gate insulating film used to form the transistor and simultaneously forming a gate insulating film in the region to be used as the film quality evaluation region, a process is performed which includes the steps of: forming a conductive film used to form a gate electrode of the transistor and then patterning the conductive film so as to form the gate electrode and simultaneously removing the conductive film from the film quality evaluation region; selectively introducing a high concentration of impurity and a low concentration of impurity into the semiconductor film via the gate insulating film so as to form the lightly doped source/drain region and the heavily doped source/drain region of the transistor, respectively, and simultaneously introducing one of the high concentration impurity and the low concentration of impurity into the semiconductor film for film quality evaluation via the gate insulating film in the evaluation region; forming the interlayer insulating film in a layer on the surface of the gate electrode and simultaneously forming the interlayer insulating film in the evaluation region, in a layer on the surface of the gate insulating film in the evaluation region; and forming a contact hole, for connection to the transistor, in the interlayer insulating film and simultaneously forming, in the film quality evaluation region, the opening in the interlayer insulating film in the evaluation region and in the gate insulating film in the evaluation region so that the semiconductor film for film quality evaluation is exposed.
In the case where the source/drain region of the above-described transistor includes a lightly doped source/drain region and a heavily doped source/drain region, it is desirable that the semiconductor film for film quality evaluation include a first semiconductor film for film quality evaluation and a second semiconductor film for film quality evaluation, the first semiconductor film for film quality evaluation being formed of the same layer as the lightly doped source/drain region and doped with the same impurity at the same concentration as the lightly doped source/drain region, the second semiconductor film for film quality evaluation being formed of the same layer as the heavily doped source/drain region and doped with the same impurity at the same concentration as the heavily doped source/drain region. This make it possible to evaluate both regions when the source/drain region of the transistor includes the lightly doped source/drain region and the heavily doped source/drain region.
To produce the active matrix substrate having the above-described structure, after forming a semiconductor film used to form the transistor and simultaneously forming the semiconductor film for film quality evaluation in a region to be used as the film quality evaluation region, and then forming a gate insulating film used to form the transistor and simultaneously forming a gate insulating film in the region to be used as the film quality evaluation region, a process is performed which may include the steps of: forming a conductive film used to form a gate electrode of the transistor and then patterning the conductive film so as to form the gate electrode and simultaneously removing the conductive film from the film quality evaluation region; selectively introducing a high concentration of impurity and a low concentration of impurity into the semiconductor film via the gate insulating film so as to form the lightly doped source/drain region and the heavily doped source/drain region of the transistor, respectively, and simultaneously introducing the high concentration impurity and the low concentration of impurity into the semiconductor film for film quality evaluation via the gate insulating film in the evaluation region thereby forming a first semiconductor film for film quality evaluation and a second semiconductor film for film quality evaluation; forming the interlayer insulating film in a layer on the surface of the gate electrode and simultaneously forming the interlayer insulating film in the evaluation region, in a layer on the surface of the gate insulating film in the evaluation region; and forming a contact hole, for connection to the transistor, in the interlayer insulating film and simultaneously forming, in the film quality evaluation region, the opening in the interlayer insulating film in the evaluation region and in the gate insulating film in the evaluation region so that the semiconductor film for film quality evaluation is exposed.
In this production method, the first semiconductor film for film quality evaluation and the second semiconductor film for film quality evaluation both have substantially the same process histories as the lightly doped source/drain region and the heavily doped source/drain region, respectively, of the transistor, and thus the film quality of the source and drain regions of the transistor can be accurately evaluated by analyzing the semiconductor film for film quality evaluation. Furthermore, in this production method, the film quality evaluation region can be formed using the production steps of producing the transistor without needing an additional step.
In the active matrix substrate according to the present invention, when the film quality evaluation region is used to evaluate the source/drain region of the transistor, it is desirable that the film evaluation region have a greater area than the source/drain region of the transistor.
In the present invention, the film quality evaluation region may be formed so as to evaluate a channel region of the transistor. In this case, the semiconductor film for film quality evaluation is formed of the same layer as the channel region of the transistor, such that the semiconductor film for film quality evaluation and the channel region are both either intrinsic or channel-doped with the same impurity at the same concentration.
To produce the active matrix substrate having the above-described structure, after forming a semiconductor film used to form the transistor and simultaneously forming the semiconductor film for film quality evaluation in a region to be used as the film quality evaluation region, and then forming a gate insulating film used to form the transistor and simultaneously forming a gate insulating film in the region to be used as the film quality evaluation region, a process is performed which includes the steps of: forming a conductive film used to form a gate electrode of the transistor and then patterning the conductive film so as to form the gate electrode and simultaneously removing the conductive film from the film quality evaluation region; selectively introducing an impurity into the semiconductor film via the gate insulating film while covering the semiconductor film for film quality evaluation with a mask so as to form source and drain regions of the transistor; and forming a contact hole, for connection to the transistor, in the interlayer insulating film and simultaneously forming, in the film quality evaluation region, the opening in the interlayer insulating film in the evaluation region and in the gate insulating film in the evaluation region so that the semiconductor film for film quality evaluation is exposed.
In this production method, the semiconductor film for film quality evaluation has substantially the same process history as the channel region of the transistor, and thus the film quality of the channel region of the transistor can be accurately evaluated by analyzing the semiconductor film for film quality evaluation. Furthermore, in this production method, the film quality evaluation region can be formed using the production steps of producing the transistor without needing an additional step.
In the active matrix substrate according to the present invention, when the semiconductor film for film quality evaluation is formed of the same layer as the channel region of the transistor such that the semiconductor film for film quality evaluation and the channel region are both either intrinsic or channel-doped with the same impurity at the same concentration, the film quality evaluation region may include a gate insulating film for film quality evaluation formed on the surface of the semiconductor film for film quality evaluation wherein the gate insulating film for film quality evaluation is formed of the same layer as the gate insulating film of the transistor.
In this active matrix substrate according to the present invention, it is desirable that the gate insulating film for film quality evaluation be exposed through an opening formed in an insulating film in the evaluation region, the insulating film in the evaluation region being formed of the same layer as an interlayer insulating film formed above the transistor.
In this active matrix substrate according to the present invention, because the semiconductor film for film quality evaluation and the gate insulating film for film quality evaluation are formed in the film quality evaluation region using the same layers as the channel region and the gate insulating film, respectively, of the transistor, film quality, such as an impurity distribution at an interface between the gate insulating film and the channel region of the transistor, can be evaluated by evaluating the film quality evaluation region. In the evaluation using the film quality evaluation region, unlike the evaluation performed directly upon the transistor, it is possible to immediately start the evaluation without having to remove the interlayer insulating film and the gate electrode, because the film quality region is exposed through the opening formed through the insulating film which is formed in the evaluation region simultaneously with the interlayer insulating film in the transistor region. This makes it possible to easily evaluate the film quality in a short time. The film quality evaluation region can be formed over a large area without influencing the characteristics of the transistor. The large area of the film quality evaluation region allows high-accuracy analysis of the film by way of SIMS.
To produce the active matrix substrate having the above-described structure, after forming the channel region of the transistor and simultaneously forming the semiconductor film for film quality evaluation and in a region to be used as the film quality evaluation region, and then forming the gate insulating film of the transistor and simultaneously forming the gate insulating film for film quality evaluation in the region to be used as the film quality evaluation region, a process is performed which includes the steps of: forming a gate electrode of the transistor and simultaneously forming a conductive film in the film quality evaluation region; forming source and drain regions of the transistor by introducing an impurity via a predetermined mask; forming the interlayer insulating film in a layer on the surface of the gate electrode and simultaneously forming the interlayer insulating film in the evaluation region, in a layer on the surface of the conductive film in the evaluation region; forming a contact hole, for connection to the MIS transistor, in the interlayer insulating film and simultaneously forming the opening in the film quality evaluation region so that the conductive film is exposed through the opening; and etching the conductive film via the opening thereby removing the conductive film so that the gate insulating film for film quality evaluation is exposed through the opening.
In this production method, the gate insulating film for film quality evaluation and the semiconductor film for film quality evaluation have substantially the same process histories as the gate insulating film and the channel region, respectively, of the transistor, and thus the film quality of the gate insulating film and the channel region of the transistor can be accurately evaluated by analyzing the gate insulating film for film quality evaluation and the semiconductor film for film quality evaluation.
The present invention also provides another method of producing an active matrix substrate, comprising the steps of: forming a channel region and a gate insulating film of the thin film transistor and simultaneously forming, in a region to be used as the film quality evaluation region, the semiconductor film for film quality evaluation and the gate insulating film in the evaluation region; forming the gate electrode and the scanning line and simultaneously forming a short-circuit line for electrically connecting at least some of the scanning line and the data line to one another and still simultaneously forming a conductive film in the film quality evaluation region; forming source and drain regions of the thin film transistor by introducing an impurity via a predetermined mask; forming the interlayer insulating film in a layer on the surface of the gate electrode and the scanning line and simultaneously forming the interlayer insulating film in the evaluation region, in a layer on the surface of the conductive film in the evaluation region; forming a contact hole, for connection to the thin film transistor, in the interlayer insulating film and simultaneously forming a cut-off hole so that a predetermined part, which will be cut off later, of the short-circuit line is exposed through the cut-off hole and sill simultaneously forming the opening in the film quality evaluation region so that the conductive film is exposed through the opening; and cutting off the short-circuit line by etching the predetermined part of the short-circuit line and simultaneously removing the conductive film by way of etching via the opening so that the semiconductor film for film quality evaluation and the gate insulating film for film quality evaluation are exposed through the opening in the film quality evaluation region. In this production method, the film quality evaluation region can be exposed using the production step of cutting off the short-circuit lines for electrostatic discharge protection without needing an additional step.
In the present invention, the area of the film quality evaluation region is considerably greater than the channel region of the transistor. More specifically, the area is as large as about 1 mm2. Therefore, in addition to elemental analysis by way of SIMS, it is also possible to evaluate crystallinity of the semiconductor film for film quality evaluation (channel region) by way of Raman scattering, or the like. Thus, the film quality evaluation region is very useful for evaluating the transistor, such as a thin film transistor formed of a polycrystal semiconductor film obtained by crystallizing an amorphous semiconductor film.
In the present invention, the semiconductor film for film quality evaluation may be formed in an area containing the area where the opening described above is formed. That is, the semiconductor film for film quality evaluation may be formed over an area greater than the area where the opening is formed. Instead, the semiconductor film for film quality evaluation may be formed inside the opening described above.
In the present invention, the transistor may be a thin film transistor, and an active matrix substrate for use in an electrooptical device, such as a liquid crystal display, may be realized by forming: an image display area including scanning lines, data lines, and pixel electrodes, a gate electrode of each thin film transistor being electrically connected to one scanning line, a source region of each thin film transistor being electrically connected to one data line, a drain region of each thin film transistor being electrically connected to one pixel electrode; a scanning line driving circuit and a data line driving circuit, disposed in a peripheral area outside the image display area, for outputting a signal to the scanning lines and the data lines; and signal lines for supplying signals to the driving circuits. If the active matrix substrate and an opposite substrate on which an opposite electrode is formed is combined together, and an electrooptical material, such as a liquid crystal, is disposed between the active matrix substrate and the opposite substrate, then an electrooptical device, such as a liquid crystal display, is obtained. In this case, the film quality evaluation region is formed at one or more locations on the substrate, where neither the image display are, the scanning lines, the data lines, nor the signal lines are formed.